US5515679AExpiredUtility

Geothermal heat mining and utilization

86
Individually held — no corporate assignee on recordPriority: Jan 13, 1995Filed: Jan 13, 1995Granted: May 14, 1996
Est. expiryJan 13, 2015(expired)· nominal 20-yr term from priority
Inventors:Gary Shulman
F24T 10/10F03G 4/074F24T 10/30Y02E10/10
86
PatentIndex Score
134
Cited by
18
References
32
Claims

Abstract

Method and apparatus for recovering and utilizing thermal energy from subterranean hot rock by means of a self-powered closed system which transfers heat from the hot rock to a relatively cool liquid, e.g. water, flowing in a heat-conducting pipe that extends in a loop descending from the earth's surface to and through the hot rock to a depth, e.g., in the range of 5,000 to 50,000 feet, and connects to the bottom of a heat-insulated riser in which the heated liquid flow ascends to the surface. The heated flow is processed at the surface to utilize recovered thermal energy and is cooled, and the cooled liquid is recycled to the hot rock. A plurality of descending pipe loops are disposed radially a horizontal distance away from said riser and each is connected to the riser. A manifold connecting said pipes at the surface permits rotation of the descending liquid among the pipe loops for continuous operation. The natural temperature of the subterranean hot rock increases with depth causing the temperature of the liquid in the pipes to increase as it descends. The heated flow in the riser ascends to the surface by thermo-siphon circulation which results from the hydraulic head difference between the descending higher density relatively cool liquid flow and the ascending lower density flow of heated liquid and flashed vapor. At the surface, the thermal energy of the heated flow in the riser is recovered and utilized, e.g., by heat exchange and/or by use of flashed vapor in a condensing power cycle, and the cooled liquid flow therefrom is recycled to the manifold and pipes for another heat gathering circuit.

Claims

exact text as granted — not AI-modified
I claim: 
     
       1. A method for recovering thermal energy contained in subterranean hot rock, comprising: a) providing an insulated conduit extending from the surface of the earth to a desired depth in said hot rock;   b) providing a plurality of heat conducting pipes, each of which extends from a manifold at a surface of the earth, through said hot rock and into a bottom of said conduit, thereby forming a closed flow path from said manifold into the bottom of said conduit;   c) heating a fluid in the form of a relatively cool liquid by passing said fluid from said manifold through at least one pipe of said plurality of pipes thereby providing a heated liquid containing thermal energy from said hot rock;   d) passing the heated liquid from said at least one pipe into said bottom of said conduit thereby providing said fluid at a top of said conduit after rising through said conduit;   e) discharging said fluid from said top of said conduit;   f) maintaining a desired wellhead pressure of the fluid in the top of said conduit;   g) maintaining a desired reduced pressure of the fluid being discharged from said conduit;   h) extracting thermal energy from said fluid after being discharged from said conduit thereby cooling said fluid and providing said relatively cool liquid; and   i) recirculating fluid from step "h" depleted in thermal energy to provide the relatively cool liquid in step "c".   
     
     
       2. A method according to claim 1 wherein said liquid is vaporizable, further comprising: j) maintaining said wellhead pressure to cause a portion of the heated liquid in said conduit to vaporize and form a hot two-phase flow of liquid and vapor as it ascends in said conduit.   
     
     
       3. A method according to claim 2, further comprising: k) separating the liquid and vapor of said two-phase flow being discharged from said conduit.   
     
     
       4. A method according to claim 3, further comprising: expanding said vapor in a turbine and condensing said expanded vapor at a further reduced pressure, thereby producing power and relatively cold liquid condensate.   
     
     
       5. A method according to claim 4, therein said separated liquid and condensate provide the cool liquid in step "i". 
     
     
       6. A method according to claim 1, wherein said thermal energy is extracted by heat exchange. 
     
     
       7. A method according to claim 2, which further comprises: k) transferring heat from liquid in step "h" by heat exchange to another fluid.   
     
     
       8. A method according to claim 1, wherein said liquid is water. 
     
     
       9. A method according to claim 4, wherein said liquid is water and said vapor is steam. 
     
     
       10. A method according to claim 1, further comprising: j) maintaining the liquid in at least one of said pipes of said plurality essentially immobile; and   k) continuously extracting thermal energy in step "h".   
     
     
       11. A method according to claim 1, wherein said liquid is an organic substance. 
     
     
       12. A method according to claim 1, wherein said liquid has a boiling point higher than that of water and is chemically stable in said flow path. 
     
     
       13. A method according to claim 1, wherein said liquid has a boiling point loner than that of water and is chemically stable in said flow path. 
     
     
       14. A method according to claim 13, wherein said liquid is selected from the class of substances consisting of ammonia, aqueous ammonia, isobutane, isopentane and fluorocarbon refrigerants. 
     
     
       15. A method according to claim 1, wherein said insulated conduit extends to a depth in the range of 5,000 to 50,000 feet. 
     
     
       16. A method according to claim 1, wherein said reduced discharge pressure is in the range of 50 to 750 psia. 
     
     
       17. A method according to claim 1, wherein said hot rock is at a temperature in the range of 300° C. to 1000° C. 
     
     
       18. A method for utilizing thermal energy contained in subterranean hot rock, comprising: a) providing an insulated conduit extending vertically from the surface of the earth into said hot rock;   b) providing a plurality of heat conducting pipes, each of which is disposed radially from said conduit and extends from a manifold at a surface of the earth through said hot rock and into a bottom of said conduit thereby forming a closed flow path from said manifold into the bottom of said conduit;   c) heating a relatively cool liquid by passing said liquid through at least one pipe of said plurality of pipes thereby providing heated liquid containing thermal energy from said hot rock;   d) passing the heated liquid from said at least one pipe into said bottom of said conduit;   e) maintaining the wellhead pressure in the top of said conduit to cause a portion of the heated liquid in said conduit to vaporize and form a hot two-phase flow of liquid and vapor as it ascends in said conduit;   f) discharging said two-phase flow from said top of said conduit;   g) maintaining a desired reduced pressure of the two-phase flow being discharged from said conduit thereby increasing the vapor content in said flow;   h) utilizing thermal energy contained in said two-phase flow after being discharged and condensing the vapor in said flow to liquid condensate, thereby cooling said flow and providing cooled liquid; and   i) recirculating said cooled liquid from step "h" to provide the relatively cool liquid in step "c".   
     
     
       19. A method according to claim 18, further comprising, in step "h": i) separating said liquid and vapor being discharged from said conduit in step "f"; and   k) expanding said separated vapor in a turbine to produce power; and   l) condensing said expanded vapor.   
     
     
       20. A method according to claim 18, wherein no subterranean environmental pollutants are released to the environment. 
     
     
       21. Apparatus for recovering thermal energy contained in subterranean hot rock, comprising: a) an insulated conduit extending from a wellhead at the surface of the earth to a desired depth in said hot rock for passing a fluid in said conduit from said depth to said wellhead;   b) a plurality of heat conducting pipes, each of which is connected at a top end through a valve to a manifold at the surface of the earth and at the other end to a bottom of said conduit forming a closed flow path from said manifold into said conduit;   c) means connected to said manifold for supplying liquid at a relatively cool temperature to said manifold;   d) throttling means connected to a top of said conduit for maintaining a desired wellhead pressure in said conduit and for maintaining a desired discharge pressure of the fluid being discharged from said throttling means;   e) means connected to said throttling means for receiving said discharged fluid and for extracting thermal energy therefrom and providing said liquid at said relatively cool temperature; and   f) means connected to the means for supplying liquid for recirculating liquid at said relatively cool temperature from the means for receiving said discharge fluid to said manifold.   
     
     
       22. Apparatus according to claim 21, wherein said insulated conduit extends to a depth in the range of 5,000 to 50,000 feet. 
     
     
       23. Apparatus according to claim 21, wherein said discharge pressure is in the range of 50 to 750 psia. 
     
     
       24. Apparatus according to claim 21, wherein the temperature of said hot rock is in the range of 300° C. to 1000° C. 
     
     
       25. Apparatus for utilizing thermal energy contained in subterranean hot rock, comprising: a) an insulated riser for passing fluid from a desired depth in said hot rock to the surface of the earth;   b) a plurality of heat conducting pipes, each of which extends from the surface of the earth to said depth and is disposed outward from the top of said riser to a desired distance from said riser and then inward to join a bottom of said riser thereby forming a closed flow path from each of said pipes into the bottom of said riser;   c) a manifold at said surface to which each of said pipes is connected through a valve;   d) means connected to said manifold for supplying liquid at a relatively cool temperature to said manifold, said liquid being capable of existing in vapor phase at elevated temperature;   e) means for passing liquid from said manifold to at least one of said pipes;   f) throttling means connected to a top of said riser for maintaining a two-phase flow of liquid and vapor discharging from said riser at a desired pressure;   g) means connected to said throttling means for receiving said two-phase flow and for extracting thermal energy therefrom and for providing said liquid at said relatively cool temperature; and   h) means connected to said manifold for recirculating liquid at said relatively cool temperature from the means for receiving said discharge fluid to said manifold.   
     
     
       26. Apparatus according to claim 25, wherein said plurality of pipes is disposed radially around said riser. 
     
     
       27. Apparatus according to claim 25, wherein the internal cross-section area of the upper part of said conduit is greater than the internal cross-section area of the lower part of said conduit. 
     
     
       28. Apparatus according to claim 25, which further comprising in the means for receiving said two-phase flow: i) separator means for separating said two-phase flow into liquid and vapor flows;   j) turbine-generator means for expanding said separated vapor and generating electricity;   k) surface condenser means for condensing said expanded vapor to liquid at a relatively low temperature and pressure; and   l) pump means for pressurizing said condensed liquid.   
     
     
       29. Apparatus according to claim 27, wherein said liquid in the means "d" is water. 
     
     
       30. A method according to claim 4, which further comprises: m) utilizing power produced by said turbine to drive a generator and produce electricity.   
     
     
       31. A method according to claim 12, wherein said liquid is selected from the class of fluids which are conventionally known as heat transfer fluids. 
     
     
       32. A method according to claim 19, which further comprises: m) utilizing power produced by said turbine to drive a generator and produce electricity.

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